TINY SONGBIRDS such as martins and thrushes can travel as far as 311 miles a day in their annual migrations between the Americas, three times as far as researchers had previously believed.
Biologists made the discovery in the first study to track the birds to their wintering grounds and back.
The birds fly two to six times as fast heading north in the spring as they do heading south in the autumn, perhaps in a competition to reach the best breeding sites and attract the fittest mates, ornithologist Bridget Stutchbury of York University in Toronto reports in the journal Science.
One industrious female martin flew the 4,660 miles from the Amazon basin to Pennsylvania in 13 days, with four of them spent on stopovers.
The new data was obtained using miniature geolocators, about the size and weight of a 10 cent coin, attached to the birds’ backs.
The same technology was used in 2006 by Scott Shaffer of the University of California, Berkeley, to demonstrate that shearwater gulls fly a massive figure-eight-shaped pattern over the Pacific Ocean during their migration, travelling as many as 46,000 miles in a year.
But the gulls are much bigger. Ms Stutchbury’s paper marks the first time a newly miniaturised version of the geolocator has been used on birds so small.
Small birds have been difficult to track in the past. Radar can monitor large flocks for short distances but not individual birds, and the birds are too small to be tracked by satellite.
Some researchers have attached radio transmitters and attempted to follow birds in aircraft.
One German researcher was able to follow individual birds for as long as four days.
The new geolocators were developed by James W Fox and his colleagues at the British Antarctic Survey.
The self-contained units, weighing about 1.3 to 1.5g (the birds themselves weigh about 50g), carry a computer chip and a light-sensor mounted on a small stalk that sticks up above the feathers.
The sensor measures and records the times of sunrise and sunset.
“For any given place on the planet, we know the times of sunrise and sunset, so we can match up the locations,” Ms Stutchbury said.
On their return to their breeding grounds, the birds are captured and the data downloaded.
Preliminary studies showed that the devices do not interfere with the birds’ mobility or their ability to catch prey, mate and feed offspring. The martins flew the 1,500 miles south to the Yucatan Peninsula in five days, then stopped over for three or four weeks before continuing on to the Amazon basin.
The thrushes spent one to two weeks in the southeastern United States before continuing on to their wintering grounds in a narrow strip along the coast of Honduras or Nicaragua.
The research was sponsored by the National Geographic Society.